Grave situation's beginning: euro is destabilised (7)
I believe the answer is:
serious
'grave' is the definition.
(I know that grave can be written as serious)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for serious that I've seen before include "Not light or frivolous" , "Important -- grave" , "Important - solemn" , "Earnest; vital" , "Solemn, thoughtful" .)